Title: Image-directed nanoscale photo-crosslinking for the study of subnuclear structures Mammalian genomes encode genetic information in linear sequence, yet proper expression of cell-specific genes depends on higher order nuclear organization, from the folding of chromosomes to the assembly of chromosomal domains and nuclear compartments. Defining the dynamic assembly, structure and interaction of these sub-nuclear components is critical to understanding the basic mechanisms of cellular functions and regulations. Cutting-edge imaging methods are revealing the details of the nucleus at increasingly higher resolutions; genomic methods such as Hi-C enable genome-wide analysis of chromatin folding and interactions at the molecular level. However, few technologies are available to integrate the imaging and genomic analyses together. The proposed studies aim to develop an image-directed nanoscale photo-crosslinking technology (INPX) to instantly capture genomic DNA in a selected nuclear volume to enable high resolution spatial and temporal studies of sub-nuclear structures at the single cell level. INPX will greatly facilitate the structure and function study of nuclear organization and subnuclear compartments. !